Electron gun device



June 18, 1968 SUSUMU YOSHIDA ETAL ELECTRON GUN DEVICE Filed April 6,1965 2 Sheets-Sheet 1 Intel-L77: rs

Susumu Yoshida Hiroki 5(11'0 June 18, 1968 SUSUMU YOSHIDA ETAL 3,389,290

ELECTRON GUN DEVICE Filed April 6, 1965 v 2 Sheets-Sheet 2 InzeQnTbrsSusu mu Yosh z'da.

Hiro/czi Said? United States Patent O 3,389,290 ELECTRON GUN DEVICESusumu Yoshida, Tokyo, and Hiroki Sato, Ituma-gun, Saitama-ken, Japan,assignors to Sony Corporation, Tokyo, Japan, a corporation of Japan iFiled Apr. 6, 1955, Ser. No. 446,054 6 Claims. (Cl. 313337) ABSTRACT OFTHE DISCLOSURE Electron emitter assembly wherein a graphite heatingelement is connected to a lead consisting predominantly of nickel by anintermediate layer including an integral carbide of a refractory metaland an alloy of nickel and the refractory metal.

The present invention relates to an electron emitter assembly of thetype employed in vacuum tubes and electron guns for cathode ray tubes.

Recently, graphite heating elements have been employed in such tubes andelectron guns, and high density, non-porous graphite materials have beendeveloped for this purpose. The graphite is characterized by highdensity, high resistivity, high thermal stability, and great mechanicalstrength. The use of such graphite provides a good heating source for anelectron gun device. However, since graphite itself is very stablechemically, it is almost impossible to attach lead wires of, forexample, nickel or the like to the graphite heating surface for formingan ohmic contact therewith. The electrodes are sometimes mechanicallycontacted with the graphite heater, but such contact is unstable, andvariations in the contact resistance are caused, thereby causing anon-uniform characteristic in the heater.

In view of the foregoing, one of the objects of the present invention isto provide an electron emitter assembly in which a lead is attached to agraphite type heater by means of a'metallurgical bond.

Another object of the invention is to provide an electron emitterassembly in which the electron emissive material is secured to agraphite heater through an intermediate stable carbide layer.

Another object of the invention is to provide a method of attachingnickel or nickel base alloys to a g p ite surface by means of anintermediate carbide zone produced in situ.

The improved electron emitter assembly of the present invention includesa graphite heating element, and a metallic lead secured to the graphitehaving an intermediate layer containing a stable metal carbide formedintegrally with the graphite heating element, and an electron emissivematerial secured to the graphite heating element, the emissive materialalso preferably being secured to the graphite by means of theintermediate carbide layer.

A further description of the present invention will be made inconjunction with the attached sheets of drawings in which:

FIGURE 1 is an enlarged plan view illustrating somewhat schematicallythe principal portions of a graphite heater assembly produced accordingto the present invention;

FIGURE 2 is a cross-sectional view taken along the line II--II of FIGURE1, showing the heater structure combined with a grid;

FIGURE 3 is an enlarged, partial cross-sectional view of a portion ofthe heater assembly of the present invention;

FIGURE 4 is a schematic, greatly enlarged cross-sectional viewillustrating the manner in which cathode ma- 'ice terials are attachedto the graphite heater in accordance with this invention;

I FIGURES 5A and 5B are views in elevation of modified forms of thegraphite heater structure;

FIGURE 6 is a plan view of another modified form of the inventionillustrating the manner of securing the graphite heater to the supportto permit thermal expansion of the heater in its lengthwise dimension;and

. FIGURE 7 is a cross-sectional view taken substantially along the lineVII-VII of FIGURE 6.v

As shown in the drawings:

The heater structure of the present invention has been shown in theenvironment of an electron gun for a cathode ray tube for purposes ofexample. In FIGURE 1, reference numeral 1 has been applied to a ceramicheader, across which there is a graphite heater strip 2. An electronemissive material 3 such as a combination of barium and strontium oxidesis disposed on a nickel base plate 4 and is secured centrally of thegraphite heater strip 2 in a manner which will be explainedsubsequently.

The graphite heater strip 2 has enlarged end portions 5 at both endsthrough which holes 6 extend. The upper surface of the header 1 has apair of opposed grooves 7 formed therein in which the enlarged portions5 of the graphite strip are received. The enlarged portions 5 may besuitable cemented to the header 1. An electrically conductive lead 8extends through a hole 9 formed in the header 1, and its upper endextends into the hole 6 of the graphite heater 2.

Referring to FIGURE 2, reference numeral 10 refers to a grid disposedabout the electron gun device, having a centrally disposed aperture 11for the passage of electrons. A spacer 12 extends between the header 1and the grid 10, and an annular retainer 13 composed of an insulatingmaterial spaces the grid 10 with respect to the outer periphery of theheader 1.

In accordance with the present invention, the leads 8 are preferablymade of nickel, or a nickel base alloy such as nickel-cobalt, ornickel-iron, the alloys containing at least 50% nickel. The leads areinserted into the aperture 6 of the graphite heater element 2. Prior toinsertion, the lead 8 is coated with a material which forms a stablecarbide with graphite, particularly a metal such as molybdenum,tungsten, titanium, vanadium, tantalum, niobium, zirconium or chromium,or other alloys. These metals are applied to the lead as a powder incombination with an organic binder which holds the powder onto the lead.This suspension of the metal particles in the binder can be appliedin'the form of a paste or can be painted or sprayed on the graphiteheater to form a layer identified at reference numeral 14 in FIGURE 3interposed between the lead 8 and the heater 2. The assembly is thenheated to an elevated temperature, usually in the range fr m about 1100C. to 2000 C. in a non-oxidizing atomsphere which may be vacuum, or aninert atmosphere such as hydrogen or nitrogen, argon, krypton, or thelike. The metal 14 and the carbon of the graphite heater 2 thereuponform a carbide containing layer 15 which is diffused into the body ofthe graphite and which firmly joins the lead 8 with the heater element2. When molybdenum is employed as the metal, the alloyed layer 15 mayinclude a carbide such as MoC or Mo C, or both. The metal of the lead -8and the carbide forming metal also form an alloy between them, firmlyjoining the two together, resulting in a metallurgically bonded unionbetween the metal of the lead and the graphite of the heater element.

FIGURE 4 of the drawings illustrates a greatly enlarged view of acathode assembly produced according to the present invention. Anelectron emission device 3 consisting of a mixture of barium oxide andstrontium oxide or the like, is deposited on a base metal 4 composed,

for example, of nickel, and the base metal 4 is mounted on a graphiteheater 2. The nickel base 4 is attached to the graphite heater 2 throughthe interposition of a carbide forming metal layer 14'. Upon treatmentof the assembly at the elevated temperature condition specifiedpreviously, .a carbide layer 15' appears between the carbide 2 and theintermediate metal layer 14, providing a secure metallurgical bondbetween the two.

FIGURE 5A illustrates still another example of a graphite heater of thepresent invention in which the thickness of the graphite heater 2 isdecreased by providing a concave portion 16 centrally of the lengthdimension of the heater 2, and positioning the cathode material 3 abovethis reduced thickness portion. This type of structure has been found toenhance the efficiency of the heater elements. In FIGURE 5B, theunderside of the graphite heater has been rounded to provide a curvedface 17 for the same reason.

FIGURES 6 and 7 illustrate a modified form of the invention in which thegraphite heater 2 is permitted to expand upon heating in the directionof its length. For this purpose, the heater 2 is mounted in spacedrelation to the header 1. One end of the graphite heater 2 is mountedsecurely to the header 1, while the other freely extends into a slot 21of greater width than the width of the graphite heater 2. One of theleads 8 may be of typical circular configuration, while the leadattached to the free end of the graphite heater 2 takes the form of anickel foil 18 joined to the graphite heater 2 at a junction identifiedat reference numeral 19. The other end of the foil 18 is cemented at thebase of the header 1 as by means of an adhesive cement layer 20. Thefoil 18 is joined to the heater 2 by means of the metallurgicalcarbide-containing bond identified by a carbide layer 15. Typically, thediameter of the lead 8 ranges from about 0.4 to 0.6 millimeter, and thethickness of the nickel foil may be 0.05 millimeter by 1.2 millimetersin cross-section.

The type of graphite preferred for use in accordance with the presentinvention has the following characteristics:

Limiting temperature C 3000 Resistivity microhm-cm l000 Thermalconductivity Kcal./m./hr./C 15 Thermal expansion coefiicient per C 3.010 Modulus of elasticity kg./mm. 2000 Bending strength kg./cm. 500

Graphite of the above characteristics is cut and processed into adesirable shape. A typical size is a length of 10 millimeters, and arectangular cross-section measuring 1.2 millimeters by 0.2 millimeter.In preparing the bonding agent, a mixture of fine powders of tantalumand molybdenum may be combined in a ratio of 1:1 by weight, and mixedwith nitrocellulose and N-butyl acetate and then applied to the metalliclead, or as a coating on the apertures 6 of the graphite heater. Theresulting assembly is heated, with the temperature being raised at therate of about 30 C. per minute, and maintained in vacuum at 1600 to 2000C. for 20 to 30 minutes. The result is the production of an alloyedlayer containing stable metallic carbides. The nickel lead may be bondedto the carbide forming metal by resistance welding at the contactpoints. The resultant heater may be mounted on a ceramic header such asshown in FIGURE 1 by cement composed principally of aluminum phosphate.Then, the surface of the heater is subjected to lapping by means ofparafiin wax. Through the lapping operation, the thickness of the heateris reduced to about 0.1 millimeter.

As another example, fine powders of nickel, molybdenum, and titanium inthe ratio of 7 to 2 to 1 by weight were mixed with the above mentionedbinder, and applied to the nickel lead which was then laid on thegraphite surface. The assembly was maintained at 1300 to 1500 C. in areducing atmosphere. S nce nickel has a low melting point, the surfaceof the alloyed layer is covered with a nickel layer. Accordingly, theunion between the nickel leads and the graphite was secured and readilyachieved.

It should be evident that various modifications and variations can beeffected without departing from the scope of the novel concepts of thepresent invention.

We claim as our invention:

1. An electron emitter assembly comprising a graphite heating element,support means carrying said graphite heating element, a metallic leadconsisting principally of nickel secured to said graphite by anintermediate layer containing a stable metal carbide formed integrallywith said graphite heating element, said lead and the metal of saidcarbide forming an alloy therebetween, and an electron emissive materialsecured to said graphite heating element.

2. The assembly of claim 1 in which said metal carbide is a carbide of ametal selected from the group consisting of molybdenum, tungsten,titanium, vanadium, tantalum, niobium, zirconium, and chromium.

3. The assembly of claim 1 in which said electron emissive material isbonded to said graphite through a metal carbide integrally formed insaid graphite.

4. An electron emitter assembly comprising a graphite heating element,support means carrying said graphite heating element, a metallic leadconsisting principally of nickel secured to said graphite and having anintermediate layer containing a stable metal carbide formed integrallywith said graphite heating element, said lead and the metal of saidcarbide forming an alloy therebetween, and an electron emissive materialsecured to said graphite heating element, said graphite heating elementbeing shaped to provide a zone of reduced thickness in the area in whichsaid electron emissive material is secured.

5. An electron emitter assembly comprising support means, a graphiteheating element secured at one end to said support and having its otherend free for accommodating thermal expansion, a metallic lead consistingprincipally of nickel secured to said graphite by an intermediate layercontaining a stable metal carbide formed integrally with said graphiteheating element, said lead and the metal of said carbide forming analloy therebetween, and an electron emissive material secured to saidgraphite heating element.

6. The assembly of claim 5 in which said metallic lead is in the form ofa metal foil.

References Cited UNITED STATES PATENTS 2,438,732 3/1948 Williams 252-5032,636,856 4/1953 Suggs et al. 313352 X 3,085,317 4/1963 Stackhouse313-311 X 2,030,695 2/1936 Erber 313-345 X 2,243,250 5/1941 Dietz313-355 X 2,263,164 11/1941 Dailey 313-355 X 2,858,470 10/ 1958 Thurber313346 X 2,904,717 9/ 1959 Kerstetter 313-355 3,073,717 1/1963 Pyle etal. 313-345 X FOREIGN PATENTS 739,251 9/ 1943 Germany.

JOHN W. HUCKERT, Primary Examiner.

A. I JAMES, Assistant Examiner.

